Conventionally, a stator of an electric rotating machine equipped with a circular-shaped stator core that has a plurality of slots arranged in a circumferential direction and a stator coil wound around the slots of the stator core is generally known.
The stator core is constituted to have a plurality of teeth projecting inwardly in a radial direction so as to divide the slots on a side of both sides in a circumferential direction.
In order to secure a resistance against vibration of the stator coil in such a stator, the stator coil is fixed to the stator core by using an impregnant, such as varnish, for example.
An impregnating method of infiltrating the impregnant into the slots of the stator core by dripping the impregnant on an end part of the coil is disclosed in JP-A-2003-189523.
By the way, as a kind of stator core, there is a stator core that is not provided with flange portions projecting in the circumferential direction at tips of the teeth in order to raise a space factor of the coil in the slots.
When the impregnating method disclosed in the JP-A-2003-189523 is adopted in such a stator core, a radially most inner side coil of the stator coil cannot be fixed firmly to the stator core.
That is because, since the flange portions are not provided in an inner side in a radial direction of the radially most inner side coil, there is no place where the impregnant can collect.
Then, in order for the radially most inner side coil to be fixed firmly, it is considered that the impregnant is dropped to an inner circumferential surface from the inner circumferential side of the stator core so that the impregnant is infiltrated into the slots, however, the following problems occur in such a case.
Although the stator core is usually constituted by a plurality of steel plates laminated in an axial direction of the core, if a corner part where a projected tip surface and a side surface of the teeth that abut is formed in straight-like planes when punching the steel plate by pressing, burrs are easily formed in the corner part.
Therefore, if the impregnant is applied to the inner circumferential surface from the inner circumferential side of the stator core, the burrs formed in the corner part become a bank, and the impregnant that remains on the inner circumferential surface (the projected tip surface of the teeth) of the stator core can easily adhere.
Thus, if the impregnant adheres to the inner circumferential surface of the stator core as a hardened material, it interferes with a perimeter part of the rotor disposed at the inner circumferential side of the stator core, and the problems such as a deterioration of the ease of assembly at the time of inserting the rotor and the impregnant being shaved off with the rotor such that it becomes a foreign substance damaging the structures, such as the stator coil and a gear, occurs.
Moreover, as other problems raised by the presence of the burrs, since it becomes easy for cooling oil to contact the teeth surface at the time of oil-cooling of the cooling oil supplied to the inside of the electric rotating machine, causing of worsening of power loss as resistance is mentioned when rotating the rotor.